1. Field of the Invention (Technical Field)
The present invention relates to attenuation of shock, particularly for items undergoing high levels of acceleration or deceleration.
2. Description of Related Art
Items that undergo large accelerations or decelerations (gun launched projectiles, crash recorders, earth penetrating items, etc.) subject their internal components to a very severe shock environment while undergoing large, rigid body base accelerations/decelerations. For example, while the average acceleration of a projectile may be on the order of 5,000 G, high frequency shocks over 10 times this level are experienced by the internal components in all three axes due to the many higher order structural modes of the projectile assembly and non-homogeneity of the target impacted. The high shock attenuation method of the invention reduces these high frequency shocks, allowing lower cost, simpler, less shock hardened constriction of the internal system components to survive the launch or impact events.
Referring to FIG. 1 (left-hand side), if one attempts to employ traditional elastomeric or other compliant isolation system materials used to attenuate and absorb high frequency components of a shock, they will structurally fail or bottom out under the large average deceleration forces present during a sustained rigid body high g acceleration or deceleration event. Because of this, traditionally items that must survive both high shocks and high levels of acceleration/deceleration are rigidly mounted in the assembly (FIG. 2), transmitting all of the acceleration and high frequency shocks to the internal items.
In the present invention, the isolation material that surrounds the item to be protected has a density close to the item to be isolated, to limit these forces to stay within the stress/strain capabilities of the isolation material, as shown in FIG. 1 (right-hand side). An exemplary embodiment is to mix very fine tungsten powder into an elastomeric isolation material until its density is close to or equal to the isolated item density, or to alter its chemical composition to increase its density. This will in effect put the item in hydrostatic balance with the surrounding material, or “float” the item in the isolation material. This will reduce the higher frequency components of the penetration shock due to higher order modes in the item and mount assembly while transmitting most or all of the base rigid body motion. The thickness of the material on the sides, top, and bottom may also be varied to alter the system response in the different axes.
No one has used density tailoring of a dampening medium to keep strains within material limits, i.e., to keep the material from “squishing out” from around the item. The present invention prefers to have the dampening material density approximately equal the isolated item density, in essence “floating” the item in the dampening medium. Furthermore, no one has successfully attained 3D shock/vibration isolation; there has only been simple bumpers employed on the end of an item